1. Field of the invention
The present invention relates to a process for the preparation of light-sensitive microcapsules.
2. Description of prior art
Light-sensitive materials comprising a light-sensitive layer containing silver halide, a reducing agent and a polymerizable compound provided on a support can be used in an image forming method in which a latent image of silver halide is formed, and then the polymerizable compound is polymerized to form the corresponding image.
Examples of said image forming methods are described in Japanese Patent Publication Nos. 45(1970)-11149 (corresponding to U.S. Pat. No. 3,697,275), 47(1972)-20741 (corresponding to U.S. Pat. No. 3,687,667) and 49(1974) -10697, and Japanese Patent Provisional Publication Nos. 57(1982)-138632, 57(1982)-142638, 57(1982)-176033, 57(1982)-211146 (corresponding to U.S. Pat. No. 4,557,997), 58(1983)-107529 (corresponding to U.S. Pat. No. 4,560,637), 58(1983)-121031 (corresponding to U.S. Pat. No. 4,547,450) and 58(1983)-169143. In these image forming methods, when the exposed silver halide is developed using a developing solution, the polymerizable compound is induced to polymerize in the presence of a reducing agent (which is oxidized) to form a polymer image. Thus, these methods need a wet development process employing a developing solution. Therefore, the process takes a relatively long time for the operation.
An improved image forming method employing a dry process is described in Japanese Patent Provisional Publication Nos. 61(1986)-69062 and 61(1986)-73145 (the contents of both publications are described in U.S. Pat. No. 4,629,676 and European Patent Provisional Publication No. 0174634A2). In this image forming method, a recording material (i.e., light-sensitive material) comprising a light-sensitive layer containing a light-sensitive silver salt (i.e., silver halide), a reducing agent, a cross-linkable compound (i.e., polymerizable compound) and a binder provided on a support is imagewise exposed to form a latent image, and then the material is heated to polymerize within the area where the latent image of the silver halide has been formed. The above method employing the dry process and the light-sensitive material employable for such method are also described in Japanese Patent Provisional Publication Nos. 61(1986)-183640, 61(1986)-188535 and 61(1986)-228441.
The above-mentioned image forming methods are based on the principle in which the polymerizable compound is polymerized within the area where a latent image of the silver halide has been formed.
Japanese Patent Provisional Publication No. 61(1986)-260241 describes another image forming method in which the polymerizable compound within the area where a latent image of the silver halide has not been formed is polymerized. In this method, when the material is heated, the reducing agent functions as a polymerization inhibitor within the area where a latent image of the silver halide has been formed, and the polymerizable compound within the other area is polymerized.
Further, Japanese Patent Provisional Publication Nos. 61(1986)-73145, 61(1986)-275742 and 61(1986)-278849 describe an improved embodiment of the light-sensitive material, which employs microcapsules in which the components of the light-sensitive layer such as silver halide and polymerizable compound are contained. An amino-aldehyde resin is preferably used as the shell of the microcapsules (Japanese Patent Application No. 61(1986)-53873). Therefore, light-sensitive microcapsules containing silver halide and a polymerizable compound which are encapsulated with a shell comprising an amino -aldehyde resin have been preferably employed in the light-sensitive material.
In a process for the preparation of the above-mentioned light-sensitive microcapsules, the silver halide and polymerizable compound are encapsuled with the shell in an aqueous mdeium preferably in the presence of an anionic protective colloid. The anionic protective colloid has a function of finely and uniformly dispersing the silver halide and polymerizable compound in the aqueous medium and keeping thus dispersed state. Examples of the anionic protective colloid are similar to those employed in preparation of a conventional microcapsule, such as a styrenesulfonic acid type polymer described in Japanese Patent Provisional Publication No. 56(1981)-51238 and methyl polygalacturonate (e.g. pectin) described in Japanese Patent Provisional Publication No. 60(1985)-87321.